People vacuum pack their foods to either retain fresh flavor or preserve food that would otherwise be thrown out. As such, the amortized cost of vacuum packing apparatus must be less than the cost of the food that users are trying to preserve. Further, the net savings must outweigh the inconvenience and time it takes to perform the vacuum packing operation. These economic factors dictate that vacuum packing systems be inexpensive and easy to operate. Further, they should be sufficiently compact to conveniently fit in crowded kitchens. Finally, vacuum packing systems must be reliable and consistently retain vacuums for extended periods.
With the exception of hermetic seals, all seals leak —it's just a matter of how slowly they leak. However, using appropriate materials with compatible lubricants, and applying sufficient sealing pressure, the leakage rate can be controlled to a level acceptable for the particular application.
Although the prior art is replete with simple and reliable mechanisms for evacuating air from containers, it contains few instances of simple and reliable mechanisms for readmitting air into vacuum containers. All air evacuation systems involve some sort of check valve —a generic term for a device that only allows fluids to flow in one direction. In contrast, air reentry systems can readmit air either through the same check valve that exhausted it (internal to the check valve), or through a path external to the check valve. The latter approach is inherently more reliable because making a check valve work in both directions compromises its effectiveness in at least one of the two directions. Further, bi-direction check valves generally require additional mechanisms that make them more complex and more expensive.
The internal and external are reentry approaches are illustrated in the sample of prior art examined in the following paragraphs. The internal air reentry approach embodied in U.S. Pat. No. 4,142,645 by Walton is simple, but cannot work as described. Walton discloses a check valve consisting of a ball 34 residing in an elastomeric nipple 32 featuring a conical bore 42, and a valve seat 44 having a relatively small slant angle of approximately 5 degrees. A major issue with the Walton device is the plausible impossible approach for readmitting air. Walton postulates that “pinching the nipple 32 immediately below the level of the ball 34” will deform the valve seat 44 into an elliptical or oval shape in transverse cross section, thereby creating an air reentry path between the ball and the elastic tube. See FIG. 5. This postulate is false. Although pressing on a hollow plastic tube will certainly flatten it out, pressing on a plastic tube containing a snugly-fitting ball 34 will not. This is because the ball 34 prevents diametric contraction of the tube in the vicinity of the ball, and diametric contraction in one direction must occur for the tube to expand in the perpendicular direction. Thus the circular tube cross section will remain circular, and the tube will simply compress tighter around the ball 34. Although an artist can easily draw a ball positioned in an oval-shaped cross section (FIG. 5), no such oval can be physically realized until the ball 34 is pushed out of intimate contact with the nipple 32. Pressing sufficiently hard on the elastomeric tube can generate axial forces on the ball 34 that act to move the ball 34 up the tube. However, such axial forces will be resisted by atmospheric pressure as well as frictional forces between the nipple 32 and the ball 34 that are especially large if the nipple 32 has a small slant angle. Grossly compressing the nipple 32 can force the ball 34 into a larger conical section of the nipple 32, but such compression can also pinch the tube completely closed, shutting off the air reentry path. Hence, Walton failed to disclose a combination of geometries and material properties of the nipple 32 and ball 34 that would allow the proposed air reentry method to work as postulated.
U.S. Pat. No. 6,619,493 B2 by Yang is another example of a two-way check valve that readmits air through a path internal to the check valve. The Yang approach is sound mechanically, but overly complex. Yang's approach consists of a curved diaphragm called a membrane piece 41 that rests atop a plurality of air holes 403 that lead to the inside of the container body 2. Drawing a vacuum causes the membrane piece 41 to lift and allow air to flow out of the container body 2 and through the suction hole 32. The membrane piece 41 has an integral pull rod 412 that is lifted upward by pressing on a push button 34 attached to the top of the cover 3. Lifting the pull rod 412 upward unseats the membrane piece 41 allowing air to re-enter the container body 2. The Yang apparatus for readmitting air will work, but consists of at least nine custom made parts, thereby increasing both complexity and cost. Further the housing 40 must be bonded air tight to the cover 3, and Yan mentions using a high-frequency welding machine to create such a bond. Hence the complexity and special manufacturing operations drive up cost and thereby diminish the value to would-be users.
U.S. Pat. No. 5,405,038 by Chuang is another example of a two-way check valve that readmits air through a path internal to the check valve. The silicon piece 26 is a diaphragm that naturally opens upward during the air evacuation phase. For the air reentry phase, the user presses on a separate T-shaped button 27 that forces the center of the silicon piece 26 down and its edges up, thereby creating an air leakage path. Once again, the need for a number of additional ancillary components, plus their associated assembly operations, adds complexity and cost to the air reentry mechanism.
U.S. Pat. No. 6,131,753 by Lynch is an example of an air re-entry mechanism that is external to the check valve. The air re-entry path is via a center valve opening 34. A spring 108 forces a ball 106 against the center valve opening 34, thereby keeping it closed when the container is under vacuum. The vacuum is released by pulling up on a cable 112 that has one end attached to the ball 106 and the other end attached to a pull ring 104. Lynch's valve relief assembly 100 consists of at least six different custom parts that must be manufactured and assembled to accomplish the air reentry task. Thus the Lynch device suffers from the same inherent cost penalty as the Yang device.
Air reentry systems must retain vacuums when the air reentry mechanisms are not in operation. Hence, a designer needs a quantitative understanding of how an air reentry system must be designed to preserve a vacuum. A commonly used method for retaining vacuums is to use elastomeric seals. However, to effectively retain a vacuum, the elastomeric seal member must be compressed sufficiently to limit leakage to an acceptable rate. More specifically, the elastomeric seal member must be lubricated and compressed sufficiently, in terms of pounds per linear inch, depending on the material properties of the elastomeric sealing material and the acceptable leak rate. For example, O Rings used as face compression seals typically have a Shore A Hardness of 70 (which represents a compromise between compressibility and durability). Face compression O Rings must be compressed between 20% and 30% to produce a sufficient load, measured in pounds per liner inch, to create long-lasting seals. For an O Ring having a Shore A Hardness 70, and a cross sectional diameter of 0.103 inches, the minimum recommended compression load is approximately 10.3 pounds per linear inch. Accordingly, for a standard AS568A-107 O Ring, that has a mean diameter of 0.309 inches, the total force required to achieve 10.3 pounds per linear inch is 9.99 pounds. This load can be generated by a combination of atmospheric pressure and force applied to the check valve for on external source. In the case of the AS568A-107 O Ring, the maximum load obtainable from atmospheric pressure is 1.1 pounds. This means that 8.9 additional pounds must be applied to the O Ring. This may be done with a spring-like mechanism that anchors the assembly together. This disclosure refers to such a spring-like anchor element as a retainer member. Thus, in the general case, the minimum number of parts to evacuate air from a container using an off-the-shelf check valve is three: a check valve, an elastomeric seal member, and a spring-like retainer member. The objective of this invention is to implement the vacuum release (air re-entry) mechanism with such a minimum number of parts.
Air may be readmitted into a vacuum container outfitted with a check valve and elastomeric seal member in one of three ways. The first way is to install a completely separate mechanism that may be opened and closed, such as a plug that fits into a valve or hole. This method is straight forward but requires two additional parts. A second method is to pull up on the check valve with sufficient force to unseat the elastomeric seal member. There are several disadvantages of this approach. First, a relatively high pulling load is required for even a small elastomeric seal member. For example, as already noted, the AS568A-107 O Ring requires a pre-load of approximately 9 pounds to retain a vacuum, and overcoming this large a force may be difficult for some users. A second disadvantage is the high pulling force may damage the retainer member, check valve, or the container lid. Finally, the check valve might have to be outfitted with a loop or some other pulling device to allow users to get a sufficiently strong grip on the check valve.
A third approach is not to unseat the elastomeric seal member at all, but rather lower the compressive load over a segment of the elastomer seal to allow air to leak between the elastomeric seal member and the container lid or container wall. This is the preferred approach and the one disclosed herein. This approach can be implemented by applying a lateral load to the side of the check valve. Doing so causes the check valve to tilt away from the applied load, thereby increasing compression on the opposite side of the elastomeric seal member, and decreasing compression on the side of the elastomeric seal member where the load is applied. The advantage of this approach is that it requires no additional parts. The only requirements are (1) the elastomeric seal member be sufficiently thick, and the check valve diameter be sufficiently small, to allow the check valve to tilt enough to greatly relieve the pressure on a segment of the elastomer seal, and (2) the retainer member be flexible enough to permit such movement. For example, for an AS568A-107 O Ring having a 0.103 inch thick uncompressed cross section and a 0.309 inch mean diameter, the check valve would have to be free to tilt approximately 7.6 degrees to decompress one segment of the O Ring. Accordingly, the check valve diameter must be small enough not to contact the lid when the check valve is tilted 7.6 degrees, and the retainer member must allow such a range of motion.
Prior art has not considered selectively lowering the contact pressure on one segment of an elastomeric seal member to allow air to leak past the elastomeric seal member. This is because elastomeric seal members such as O Rings are primarily intended to prevent fluid flow, not enhance it. In those instances of the prior art wherein an elastomeric seal member had to act as a switch, allowing fluid to flow past it on command, the conventional practice was to completely unseat the elastomeric seal member by disengaging it from the mating part.
In summary, a reliable and cost-effective method is needed for readmitting air into vacuum containers. The ideal method would not require a separate plug, cover, or any other ancillary part to prevent air from re-entering the vacuumed container. Such a method and apparatus are disclosed in the present invention. The present invention addresses the complexity and cost issues of prior art by devising an air re-entry system that consists of only three parts. Further, all three parts are commonly available, off-the-shelf components that can be supplied by multiple vendors. This not only avoids investments in custom manufacturing tooling, but also allows the present invention to benefit from economies of scale associated with off-the-shelf parts.